How Much Does it Cost to Run an Air Conditioner?

Tim K.

19:36, 10 December 2014

52595

Air conditioning is responsible for over 50% of your electric bill in Santa Clarita during the summer, so it might not come as a shock to you that one of our most common questions is, how much does it cost to run an air conditioner? The answer can be a bit in-depth. If you’ve read some of our articles, then you know that All Systems Mechanical is a small, U.S. Veteran-Owned business located in Southern California, and we pride ourselves on giving straight, honest answers – we have built our reputation on it. In order to figure out how much it costs to run your air conditioner, you will first need to become familiar with a few basic HVAC terms and concepts. For those of you just looking for a quick answer, I will tackle the topic of how much it costs to run your air conditioner in three different sections: HVAC concepts you must know to make this calculation, a quick rule-of-thumb way to make a cost calculation, and part three will be the in-depth, advanced calculation of how to figure out how much it costs to run your air conditioner.

How Much Does it Cost to Run an Air Conditioner – Terms & Concepts

Before we can tackle the cost of running an air conditioner, we first have to become familiar with a few of the terms and concepts we will use to make the calculation. Don’t worry – this will stay very gentlemanly and easygoing.

BTUs

A BTU stands for British Thermal Unit, which is the unit that is used in air conditioning and heating to measure the cooling power of an air conditioner. Simply put, one BTU is the amount of energy that is required for your air conditioner to cool one pound of water by one degree Fahrenheit. So how many BTUs does your air conditioner come in at? That is one of the things that you have to figure out, but it’s easier than you think: all you have to know is the size of your air conditioner.

Your air conditioner is measured in ‘tons.’ One ton is equal to 12,000 BTUs of cooling power. So, if you have a three ton unit (the average sized unit in Santa Clarita, California) then your air conditioner has 36,000 BTUs of cooling power:

3 tons X 12,000 BTUs/ton = 36,000 BTUs

If you don’t know what size your air conditioner is, you can just Google your model and number which is listed on the tag and it will tell you.

Ampere

An Ampere is a unit of measurement used to measure how many electrons (electricity) have passed a single point in a given unit of time. If you want to nerd-out on Amperes, visit the Wiki site: Ampere, but one Ampere (aka an ‘Amp’) is a really large, fixed number of electrons (6.241X10^18) crossing a circuit in one second. It’s a measure of how much electricity is flowing.

Watt

A Watt is defined as one Joule of energy per second, and is the amount of energy actually transferred over time. Again, we don’t need to go too in depth for today’s discussion but if you want to, feel free to on the Wiki page: Watt. 1,000 Watts is known as a “Kilowatt.”

Volt

A Volt is simply a measure of the electric potential between two points on a wire. That’s all you really need to know, but if you want to be technical, it is the amount of electric potential between two points when one Amp moves one Watt worth of electricity between those two points.

So why the heck is this painful flashback to high school physics necessary? Because I need to introduce you to something that you have probably already heard of, but never fully understood: the Kilowatt-Hour, which you will be using to calculate the cost of running an air conditioner.

Kilowatt-Hour

Now that you know what a Kilowatt is, you can figure out that a Kilowatt-Hour is just the number of Kilowatts used in one hour. This is the basis for how your electricity usage is measured. That little meter on the side of your house and the numbers on your electric bill are all Kilowatt-Hours, and now that you know what it is, you will be able to figure out how much it will cost to run an air conditioner.

The Basics: How Much Does it Cost to Run an Air Conditioner

This section is on how to calculate the cost to run an air conditioner quickly using a rule-of-thumb method. If you want to know the exact amount that you are paying for your air conditioner, breeze through this and then go to the next section.

Step 1 – Calculate the Amps Drawn by Your Air Conditioner

This part will vary greatly based on what the SEER rating of your unit is (see: SEER vs EER), and its size and manufacturer, so I will re-emphasize that this is a quick, layman’s guide to calculating the cost of running your air conditioner. For this guide, the average amps drawn by a modern air conditioner is illustrated below and based on a SEER-16 rating (average air conditioner):

2-Ton Air Conditioner – 15 amps

3-Ton Air Conditioner – 18 amps

4-Ton Air Conditioner – 21 amps

Write this down because you will need it in later steps.

Step 2 – Calculate the Wattage Used by Your Air Conditioner, Followed by Kilowatt-Hours

The calculation for figuring out the cost of running an air conditioner includes the number of Watts that you use as well. To figure this out, simply multiply the amps from step 1 by the voltage of your outlet. For this general price estimate, we will use a standard 240 volt power outlet which is the average size for a central air conditioner. If you have a window air conditioner, then use 110 volts.

For instance, a 3-ton central air conditioning unit would look something like this:

18 amps X 240 = 4,320 Watts

To calculate Kilowatt-Hours, divide the number that you just calculated by 1,000 to find out one Kilowatt-Hour for your air conditioner:

4,320 Watts / 1,000 = 4.32 Kilowatt-Hours

Step 3 – Find the Average Price per Kilowatt-Hour for Your Region

Take a look at the graph below and figure out the average cost per Kilowatt-Hour based on your geographical region:

For our example today, we will use Santa Clarita, California which would have an average cost per Kilowatt-Hour of 14.37 cents. Next, multiply the Kilowatt-Hours found in step 2 by this price to find out how much it costs to run your air conditioner for one hour. Then multiply it by 24 to find out how much it costs for a day, and then by 30 to find out how much it costs to run your air conditioner for a month.

4.32 X 14.37 = 62 cents an hour,

62 X 24 = $14.89 per day,

$14.89 X 30 = $446.96 per month,

But wait! That is way more than how much I pay for my entire electric bill each month! How is this possible? That is because this is the price of running your air conditioner continuously for a month.

Step 4 – Find Your Multiplier

Like I said in step 3, you have just figured out the cost to run an air conditioner for a given period of time non-stop, but your air conditioner doesn’t run all of the time! It only runs when the temperature on the thermostat goes above the temperature you have set. In fact, if you were to set your thermostat for 100 degrees then your cost for air conditioning would be $0, because your air conditioner would never run. As such, the following multipliers can be used. There is no exact way to calculate the proper multiplier and this is where the equation kind of starts to break down a bit. Every day has a different outside air temperature, humidity level, etc.

However as a general guide, you can use the following multipliers based on an indoor household temperature of 70 degrees Fahrenheit, a properly sized air conditioner, and based on the assumption that the temperature drops 20 degrees at night:

Average Outside Daytime Air Temperature – Multiplier

110 degrees – 0.8

100 degrees – 0.4

90 degrees – 0.3

80 degrees – 0.25

The purpose of the multiplier is to estimate how often your unit is actually running. For our example, we will use an average outside air temperature of 100 degrees (standard for a Santa Clarita summer):

Save Money on Your New Air Conditioner. Watch This Short Video on How:

The Advanced Way to Calculate How Much it Costs to Run an Air Conditioner

Tag – Look for Related Load Average (RLA)

The advanced way of calculating how much it costs to run an air conditioner is the same process as explained in the basic section, only in this case we will be replacing a few of our estimates with actual numbers. There are two numbers that we will now be using in our calculation that were just estimates before: the amps your air conditioner draws, and the cost per Kilowatt-Hour in your area.

The related load amperage (RLA) is the the actual number of amps that your AC draws when running. It can be found on your air conditioner’s data tag (see pic) which is located on your air conditioner. As you can see, the RLA for this unit is 27.1 amps and should be used instead of the rough numbers given in the above, basic example. As you can see, the tag from this unit is from an older air conditioner that is larger and inefficient, so our calculation is already that much more accurate! Notice on the tag, the section that says “RLA” and write this down for your unit. Don’t bite off on some of the other “maximum” and “minimum” amperage numbers. RLA is what you are looking for. Also see:

Calculate Cost per Kilowatt-Hour

As you can see in this pic, your costs per Kilowatt-Hour (kWh) can vary based on the day and your location. The easiest way to calculate this is to take the total amount of your electric bill, subtract the base fees, surcharges and taxes, and divide by the number of Kilowatt-Hours used. For this example, you can see that the total Kilowatt-Hours used was 2,215 kWh:

Final Advanced Calculation of Air Conditioning Cost

I will not take you through all of the steps again because they are the same as in the basic section, but here is what the same calculation above would look like using the advanced numbers that we just calculated:

Watts:

27.1 X 240 = 6,504

Kilowatt-Hours:

6,504 / 1,000 = 6.50 Kilowatt-Hours

Cost per Hour to Run an Air Conditioner:

6.50 kWh X 8.1 cents/kWh = 53 cents or $0.53 per hour

Cost per Day to Run an Air Conditioner:

0.53 X 24 = $12.72

Cost per Month to Run Your Air Conditioner:

$12.72 X 30 = $381.60

Using the multiplier for a 100 degree Santa Clarita summer again, we get:

$381.60 X 0.4 = $152.64

That’s a $26.00 a month difference from our basic calculation, all by using actual data. Just saying…

Would You Buy a New Car Without First Seeing What a Fair Price Would Be?

I sure hope not…but people have no problem going out and paying $10,000 for a new air conditioner without first seeing what a fair price for their specific project would be. If you were shocked at how much you’re spend on air conditioning, it may be time to buy a new air conditioner. Just be careful, and do your research first. Here’s a quick, online program that can help you on your way:

Final Thoughts on How Much it Costs to Run an Air Conditioner

Figuring out how much it will cost to run an air conditioner can be a pain, but doing it just once or twice can give you some pretty good insight into where your money is going. I’d recommend playing around with some of the multipliers and figuring out how much it affects your costs for running an air conditioner. For more information on other topics like this, visit the ASM air conditioning blog. If you live in Santa Clarita or the greater Los Angeles area, click below; you might be in our service area!

The University of Virginia - 2005 / The Wharton School of Finance - 2016 / U.S. Naval Aviator 2005-2015.
At All Systems Mechanical air conditioning and heating, we believe that the experience our clients have is every bit as important as the products they receive. Simply put, our results speak for themselves, and we'd be happy to help.
If you're in the market for a new AC or furnace, make sure that you get a fair price! Try our online calculator; click the tab on the top of this page for more information.

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